This invention relates to an overdrive mechanism for use in an automatic power transmission of an automotive vehicle.
More particularly, this invention relates to an overdrive mechanism for an automatic power transmission of the type incorporating a hydraulic torque converter disposed between an engine and a change gear mechanism.
The conventional torque converter of an automatic power transmission varies the turning force automatically and in a smooth and stepless fashion in accordance with the resistance of the vehicle. However, the conventional torque converter is severely limited in a practical sense and in efficiency because of considerably energy loss arising inevitably from fluid friction during the passage of fluid through the torque converter or from turbulence caused by a drastic change in the direction of flow of the fluid. Even when a conventional overdrive device is employed in this type of automatic transmission, no satisfactory improvement in fuel efficiency can be attained because the engine power continues to be transmitted automatically through the torque converter at the time of overdrive.
Accordingly, it is a primary object of this invention to provide a new and improved overdrive mechanism which eliminates the above-described problems of the automatic power transmission having a torque converter.
Another object of this invention is to minimize the fluctuations in the rotational force by the torque converter when not required. This usually occurs during a constant high speed operation of the engine for a long period such as in overdrive.
It is a further object of this invention to provide an overdrive mechanism which mechanically transmits the engine power to the change gear mechanism with an improved fuel efficiency by not passing through the torque converter at the time of overdrive.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the overdrive mechanism of this invention is for automatic transmissions of the type including a change gear mechanism and a torque converter having an input element connected to an engine and an output element operatively connected to the change gear mechanism, and comprises: (1) an input shaft to the change gear mechansim having a first section connected to the output element of the torque converter and a second section connected to the change gear mechanism; (2) clutch means operatively connected to the second section of the input shaft and engaging the first section of the input shaft, the clutch means being disengaged from the first section in response to a predetermined operation of the change gear mechanism; (3) a planetary gear train including (a) a sun gear, (b) a carrier operatively responsive to the input element of said torque converter, and (c) a ring gear operatively connected to the clutch means; and (4) overdrive brake means activated in response to the predetermined operation of the change gear mechanism for locking the sun gear against rotation whereby the ring gear is rotated by movement of the carrier in response to movement of the input element of the torque converter.
It is preferred that the overdrive mechanism further include a one-way clutch parallel to the clutch means for connecting the first section of the input shaft to the second section of the input shaft, the one-way clutch decoupling the second section from the first section when the speed of the second section exceeds that of the first section.
The invention consists in the novel parts, construction, arrangements, combinations and improvements shown and described. The accompanying drawing, which is incorporated in and constitutes a part of this specification, illustrates an embodiment of the invention and, together with the description, serves to explain the principles of the invention.